Multiple spot welding machines

ABSTRACT

A multiple spot welding machine suitable for the manufacture of welded wire mesh for concrete reinforcement has two pairs of bus bars supported on a transverse wall extending upwardly from a base plate of the machine. Two rows of transformers, for feeding the two pairs of bus bars, are arranged one on each side of the transverse wall. A number of electrodes are shiftable along the bus bars to any one of which each electrode is connectable. A vertically movable spring loaded bridging electrode is provided above the electrodes on the bus bars.

United States Patent 91 Ritter et al.

[541 MULTIPLE SPOT WELDING MACHINES [75] Inventors: Josef Ritter; HansGott, both of Graz, Austria [73] Assignee: EVG Entwicklungs-undVerwertungsgesellschaft m.b.H., Graz (Steiermark), Austria [22] Filed:Mar. 16, 1971 [21]. App1.No.: 124,865

[30] Foreign Application Priority Data Mar. 25, 1970 Austria ..2800/70[52] US. Cl. ..219/116, 219/56, 219/87 [51] Int. Cl. ..B23k 9/10 [58]Field of Search ..219/56, 87, 88, 116; 323/44, 323/48, 49

[56] References Cited UNITED STATES PATENTS 2,229,993 1/1941 Weightman..219/87 111 3,725,632 51 Apr. 3, 1973 1/1969 Sommeregger et al ..219/88X 1,143,220

6/1915 Mack ..219/87 Primary Examiner- C. L. Albritton AttorneyErnest F.Marmorek [5 7] ABSTRACT 6 Claims, 4 Drawing Figures PATENTEDAPM ms 3,5,5 SHEET 2 OF 4 Saf f1 5cm INVENTORS:

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ATTORNI'IY PATENTEUAPRB I975 5,532

I SHEET 3 UP 4 INVENTORI' WWW ATTORNEY PATENTEDAPM 1975 5,53

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INVENTORS. Jg fEmp an! Hans ATTORNEY MULTIPLE SPOT WELDING The inventionrelates to a multiple spot welding machine, with a system of transversebus bars fed with electric power by transformers, and with at least onerow of electrodes which can be shifted in position along the bus bars.In multiple spot welding machines of this kind each row of weldingelectrodes is served by two or more pairs of bus bars, each individualelectrode being arranged so that it can be connected selectively to anyone of the bus bars.

In large machines constructed in this way difficulties arise insupporting the total welding pressure, which is the total downwardthrust applied by all the sliding electrodes to the bus bar systemduring operation of the machine. The supporting structure tends to beexcessively massive and bulky, leaving insufficient room forconveniently accommodating the welding transformers, in particular so asto obtain short conductor leads between the transformers and the busbars. These difficulties become particularly severe if the machine isequipped with several pairs of bus bars, to allow adjustment of themachine to different operating conditions. The constructionaldifficulties are also increased if the bus bar system is subdivided intothree sections, each receiving power over a transformer from only onephase of a three-phase power supply, in order to obtain a more evenloading of the three-phase supply. Both these methods require anincrease in the number of welding transformers, making it more difficultto ac-, commodate the transformers close to the bus bar system.

In accordance with the present invention, a multiple spot weldingmachine has a system of transverse bus bars supported on a transversewall extending upwards from a base plate of the machine, two or moreelectrodes which can be shifted in position along the bus v bars and tworows of transformers for feeding the bus bar system, one row on eachside of the transverse row.

With this arrangement the welding pressure applied by the electrodes istaken by the transverse wall which can easily be stiffened sufficientlyto prevent it from bending and which takes up almost no room, measuredin the longitudinal direction of the machine. A large number of weldingtransformers can be accommodated on either side of the wall, eachtransformer being positioned close to the bus bar system, which runsalong transversely supported by the wall.

Preferably the bus bar system, which extends along the transverse wall,is subdivided into three independent sections fed by three transformers,each of which receives a single phase from a three-phase power supply.

To make the welding machine more adaptable to suit different operatingconditions, the bus bar system may consist of two pairs of bus bars, thetransformers for the one bus bar pair being positioned on one side ofthe transverse wall and the transformers for the other bus bar pairbeing on the other side of the transverse wall. This gives the shortestpossible conductor leads. The machine can be given still furtheradaptability if each section of each bus bar pair is fed by twotransformers connected, either in series or in parallel with each other,to the same phase of a three-phase current source.

Gaps between the ends of the bus bar sections are preferably staggeredalong the transverse wall so that they do not come opposite each other,that is to say so that at any given cross section through the bus barsystem not more than one gap is intersected. This allows an electrodeconnection to be provided at any desired position along the length ofthe pair of bus bars.

An example of a wire mesh welding machine according to the inventionwill now be described with reference to the accompanying drawings, inwhich:

FIG. 1 is a partly sectioned diagrammatical side view of the machine;

FIG. 2 is a diagrarnmatical front view of a lower partof the machine,seen looking in the direction of advance of the mesh;

FIG. 3 is a corresponding plan view of the lower part of the machine;and,

FIG. 4 is an example of an electric circuit for energizing thetransformers.

A base plate 1 supports a vertical transverse wall 2, which extendsright across the machine. At its top end the wall 2 supports atransverse beam 3, which in turn supports an upper vertical transversebeam 4. Mounted at each side of the upper transverse beam 4, insulatedas indicated by heavy lines, are two pairs of bus bars, the pair Sa onthe one side and the pair Sb on the other side. This system, consistingof the upper transverse beam 4 and the two pairs of bus bars isindicated in FIG. 1 by the symbol S. Of the two pairs of bus bars, thepairSa is connected over leads Za to a welding transformer Ta, the pairof bus bars Sb being connected over leads Zb to a second transformer Tb.Each transformer is supported on feet 5 on a common supporting framework6, itself supported by the base-plate 1 of the machine. All thetransformers of the welding machine are enclosed in a common housing 7which has a slot 8, through which the bus bar system S projects upwards.

The machine has a number of sliding electrodes, which can be shiftedindependently, transversely along the bus bar system S. Each slidingelectrode 11 is removably clamped between two clamping jaws 9, 10. Theupper part of the machine is equipped with a bridging electrode 12,which is retained in a holder 14 by means of a retaining piece 13. Theholder 14 is mounted on two vertical sliding rods 16, capable of slidingup and down in a hollow electrode support beam 15. The upper ends of thesliding rods 16 slide up and down in guide bushes 20, screwed adjustablyinto the upper part of the electrode beam 15. The upward slidingmovement of the electrode holder 14 is opposed by two helical springs 17mounted over the two sliding rods 16, the compression springs 17 beingsupported at their lower ends by collars 18 fixed to the sliding rods16, and at their upper ends by flanges 19 of the guide bushes 20. Whenthe machine is in operation the two helical compression springs 17thrust the upper, bridging electrode 12 downwards against the uppersurface of the workpiece, that is to say the materialof the mesh issqueezed between the upper electrode 12 and the lower electrode 11, thesprings 17 applying, adjustably, what is known as the welding pressure.

From FIG. 1 it will be seen that the total welding pressure, which isthe sum of all the welding pressure applied to the lower electrodes 11is transmitted downwards through the electrode holder 9, 10, the

upper transverse wall 4, the transverse beam 3 and the verticaltransverse wall 2 to the base plate 1. The vertical transverse wall 2 isprevented from bending by stiffening ribs which are not shown in thedrawing. It should be pointed out that this way of arranging thetransformers, in two rows on either side of the welding electrodes,provides the great advantage that twice as many transformers can beinstalled in a machine of a given width, without this involving anyincrease in the lengths of the conductor leads'between the transformersand the bus bar system S.

With reference to the plan view of the lower part of the machine shownin FIG. 3, together with the front view shown in FIG. 2, seen in thedirection of the arrow V in FIG. 3, that is to say seen in the directionof advance of the wire mesh workpiece, it will beobserved that each pairof bus bars Sa and Sb is divided into three independent and separatesections. Thus, as shown in FIG. 3, the bus bar pair Sa is divided intothe three independent sections r, s and t, the bus bar pair Sb beingdivided into three independent sections r', s, and t. The bus barsections r, s and t are separated by gaps fl and f2, the bus barsections r, s and 1 being separated by gaps fl and f2. It will beobserved in FIG. 3 that the gaps are staggered in position, so that thegap fl does not come opposite the gap f1 and the gap f2 does not comeopposite the gap f2. Consequently if a cross section is taken anywherealong the bus bar system S, this cannot intersect more than one of thegaps. This allows full electric contact to be obtained anywhere alongthe bus bar system.

In FIGS. 2 and 3 the individual transformers are represented by theletter T followed by a system of suffixes. The first suffix is theletter a or the letter b, indicating that the particular transformerfeeds the bus bar pair Sa or Sb. The second suffix indicates whichsection of the bus bar pair is fed, that is to say the section r or s ort, or on the right in FIG. 3 the section'r', or s, or t. Finally in thepresent example each section is fed by two transformers, for example thesection r is fed by the two transformers Tarl and Tar2, whereas thesection s is fed by the two transformers Tasl and Tas2, and so on.

FIG. 4 represents diagrammatically an electric circuit for feeding thetransformers. Each pair of transformers, for feeding the pair of busbars of a particular bus bar section is fed with electric power over aseriesparallel switch SP, which connects the two transfor mers together.

Each series-parallel switch SP is itself fed with power, from athree-phase supply source, over an ignitron Jg which acts as acontactless switch. The arrangement allows the two transformers for eachbus bar section to be connected together either in series or inparallel.

together in series, the transformers Tasl and Tas2 are connectedtogether in series, and the transformers Tatl and Tat2 are connectedtogether in series. This method of operation consumes the least power.

2. By this method of operating, only the three sections of the bus barsystem Sa are fed with power, but in this case the pairs of transformersare connected together in parallel, that is to say the switches SP areThe circuit shown in FIG. 4 allows power to be fed to the system in anyone of three alternative ways, to suit the particular welding job inhand. The three alternative operating 'methods are as follows:

1 By this method power is fed only to the three bus bar sections on theleft in FIG. 3, that is to say to the Sa operated in such a way thattransformers Tarl and Tar2 are in parallel, Tasl and Tas2 are inparallel, and T all and Tat2 are also connected in parallel with eachother. The power consumptionis twice as high as it is by method 1.

3. By this method all three sections of both bus bar systems Sa and Sbare fed with power, the pairs of transformers being connected togetherin parallel, by suitable operation of the series-parallel switches SP.The power consumption is four times greater than with method 1.

The alternatives provided by this method, comprising in the first placetwo or more transformers for each bus bar section and, in the secondplace, a series-parallel switch which allows the two transformers ofeach pair to be connected together either in series or in parallel,provides the great advantage that for each particular welding job thetransformers operate with the highest power factor, that is to say withthe least reactive power consumption. Consequently using a single meshwelding machine it is possible to weld with high efficiency mesh of awide variety of wire diameters.

For welding mesh of the kind which has several different wire diameters,at different locations, the following method can be adopted. Of the busbar pair Sa three sections can have their transformer pairs connectedtogether in parallel that is to say Tarl, Tar2 are in parallel, Tasl,Tas2 are in parallel and Tatl, Tat2 are in parallel, whereas for thethree sections of the bus bar pair Sb the transformer pairs are inseries. The sliding electrodes are connected to the two bus bar pairs insuch a way that the large diameter wires are welded over the bus barpair whereas the small diameter wires are welded over the bus bar pairSb. Here again the machine operates at a high power factor.

Each pair of transformers may comprise two similar windings on a commoncore, for example the pair of transformers Tarl, Tar2 may be constructedby mounting two similar windings on a common core. This gives aparticularly compact transformer construction.

The transformers for the two bus bar pairs Se and Sb are preferablyconnected to different mains transformers, that is to say the Tatransformers and the Tb transformers are connected to different mainstransformers. This arrangement gives a still better power factor.

We claim:

l. A multiple spot welding machine comprising a base plate, centraltransverse wall means extending upwardly from said base plate, a systemof transverse bus bars supported on said transverse wall means under andranged closely side by side, one of said rows of said transformersfeeding one of said bus bar pairs and the other of said rows of saidtransformers feeding the other of said bus bar pairs.

3. A multiple spot'welding machine comprising a base plate, transversewaJl means extending upwardly from said base plate, a system oftransverse bus bars supported on said transverse wall means, and tworows or transformers for feeding said bus bar system and disposed one oneither side of said transverse wall means, said bus bar system includingthree independent sections fed by three transformers each of which isadapted to receive a single phase from a three-phase power supply, eachof said bus bar sections being fed by two transformers and meansprovided for connecting said two transformers as a pair alternatively inseries or in parallel with each other to the same phase of saidthree-phase power supply.

4 A welding machine according to claim 3, wherein each of said twotransformers feeding each bus bar pair comprises one primary and twosecondary windings on a common core.

5. A welding machine according to claim 1 wherein gaps are formedbetween ends of adjacent bus bar sections and said gaps are staggered inposition along said transverse wall, whereby at any given cross-sectionthrough said bus bar system not more than one gap can be intersected.

6. A welding machine according to claim 1 further including two mainstransformers, one mains transformer feeding one row of transformers forfeeding said bus bar system and said other of said mains transformersfeeding said other row of transformers for feeding the bus bar system.

1. A multiple spot welding machine comprising a base plate, centraltransverse wall means extending upwardly from said base plate, a systemof transverse bus bars supported on said transverse wall means under andclose to a line of welding, and two rows of transformers for feedingsaid bus bar system and disposed one on either side of said transversewall means.
 2. A welding machine according to claim 1, wherein said busbar system comprises two pairs of bus bars arranged closely side byside, one of said rows of said transformers feeding one of said bus barpairs and the other of said rows of said transformers feeding the otherof said bus bar pairs.
 3. A multiple spot welding machine comprising abase plate, transverse wall means extending upwardly from said baseplate, a system of transverse bus bars supported on said transverse wallmeans, and two rows or transformers for feeding said bus bar system anddisposed one on either side of said transverse wall means, said bus barsystem including three independent sections fed by three transformerseach of which is adapted to receive a single phase from a three-phasepower supply, each of said bus bar sections being fed by twotransformers and means provided for connecting said two transformers asa pair alternatively in series or in parallel with each other to thesame phase of said three-phase power supply.
 4. A welding machineaccording to claim 3, wherein each of said two transformers feeding eachbus bar pair comprises one primary and two secondary Windings on acommon core.
 5. A welding machine according to claim 1 wherein gaps areformed between ends of adjacent bus bar sections and said gaps arestaggered in position along said transverse wall, whereby at any givencross-section through said bus bar system not more than one gap can beintersected.
 6. A welding machine according to claim 1 further includingtwo mains transformers, one mains transformer feeding one row oftransformers for feeding said bus bar system and said other of saidmains transformers feeding said other row of transformers for feedingthe bus bar system.